The wireless industry is continuously developing systems with higher data rates to satisfy the need for increased data capacity. In order to achieve higher over-the-air data transmission rates, the number of used channels is increased (i.e., higher over-the-air data rate sectorization) and a higher order modulation is used. In addition, it may be useful to alternate polarization between sectors or use polarization diversity, to enhance throughput.
Unfortunately, with an increase in the number of channels used for data transmission, interference between channels is required to be addressed. As an example, providers of wireless telecommunication technologies are required to ensure that they provide for proper wireless coverage within a specific frequency band, while minimizing interference with other frequency bands. In fact, interfering with other frequency bands may result in breaching of licenses associated with providing communication capabilities within a specific coverage area.
In order to minimize interference, a base station antenna may be required to illuminate a desired sector of transmission as uniformly as possible, while suppressing energy radiated in other directions. Unless controlled, energy may leak into undesired directions, forming small auxiliary beams called sidelobes. It is desirable to minimize or eliminate these sidelobes in order to minimize interference.
Dual polarization antennas transmit the electromagnetic energy in two orthogonal polarizations that are typically horizontal and vertical, but could also be left and right hand circular, or +/−45 degrees. The horizontally polarized component is oriented in a generally horizontal direction and the vertically polarized component is oriented in a generally vertical direction. In addition, the horizontally and vertically polarized components are oriented as orthogonal to one another. Unfortunately, controlling the distribution of radiated energy from a dual polarization antenna is difficult since vertical and horizontal polarized components experience different boundary conditions at material interfaces such as metal and plastic surfaces.
Multiple Input Multiple Output (MIMO) based systems are relatively new. They employ space-time processing to combine multiple signals in a fashion that increases total system throughput. The use of dual polarized antennas for diversity applications is well known to the industry. For example, in cellular telephony dual polarized +/−45 degree antennas are often used for diversity applications. However, their use in MIMO based systems has not been widely explored. In contrast to the antennas used for basic diversity techniques, we find that vertical/horizontal dual polarized antennas are preferred for MIMO based systems. This is due to the fact that most scatterers are either vertically or horizontally oriented. Hence, the maximum differences between signals is realized when vertical/horizontal antennas are used. This results in maximum MIMO system gain.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.